Well drilling pipe clamping apparatus

ABSTRACT

A pipe clamping apparatus for an oil well in accordance with the present invention includes a body which is formed with an opening for receiving the pipe. Two cages are mounted to the body opposite the body opening from each other. Each cage includes a pair of spaced-apart guide plates which are formed with a cam slot. A cam follower pin is inserted into the cam slot and a pair of guide arms are attached to the cam follower pin at one end. At the other ends of the guide arms, a pair of slip assemblies and one end of a retractor arm are positioned between the guide arms and attached to the cage. The other end of the retractor arm is rotatably attached to the cage via a crankshaft. Rotation of the crankshaft cause the retractor arms to pivot. The pivoting of the retractor arm causes the guide arms to move toward the body opening along a predetermined path defined by the cam slot. A pair of slips are attached to each cage for selective engagement of the pipe, according to the position of the cam follower pin within the cam slot of the cage.

[0001] This application claims priority from provisional patent application No. 60/167,935 which was filed Nov. 29, 1999.

FIELD OF THE INVENTION

[0002] The present invention pertains generally to devices for securely holding pipe structures. More particularly, the present invention pertains to devices for securing piping for oil rigs during snubbing operations.

BACKGROUND OF THE INVENTION

[0003] Oil wells are well known in the prior art for removing crude oil from the earth. Typically, a structure is built for supporting a long length of piping, and the piping is inserted into an opening in the ground and into the oil deposit for harvesting the oil. The oil is transported to the surface of the earth through the piping.

[0004] Removing oil in this manner presents some relatively unique logistical problems. Because the piping must often extend a great distance into the earth, the piping is very heavy and is difficult to control during the initial lowering of the pipe into the earth. Conversely, when the piping is in contact with a crude oil deposit within the earth, the piping becomes pressurized and is forced upward. If the pipe is not fixed in place, the pipe may be blown out of the opening, severely injuring nearby oil workers in the process. Accordingly, it is important to control the vertical motion of the piping both in the upward and downward direction.

[0005] To do this, gripping devices known in the prior art as snubbing “spiders” are included in most oil rigs for controlling vertical movement of the piping. These spiders are designed to allow movement of the piping in one direction only and are preferably deployed in pairs. One spider is attached to the piping to prevent downward movement. The other spider is inverted and attached to the piping to prevent upward movement. To move the piping up or down, one spider is opened while the other is closed and vice versa.

[0006] Spiders commonly have slip assemblies which open and close in a jaw-like action. The slip assemblies have arcuate teeth for gripping the outside surface of the piping, and have some operational problems. Specifically, because the slip assemblies are often attached to the spider at a single attachment point, the slip assemblies lose their spacing very easily with continued operation and eventually do not grip the piping tightly. For inverted spiders the slip assemblies may even fall off of the spider, with disastrous consequences (upward control of the piping is lost). What is desired is a spider design in which slip assemblies move along a constant path of travel and engage the piping in a consistent manner, each time and every time. What is further desired is a spider which can be used both in a normal or an inverted orientation.

[0007] U.S. Pat. No. 4,355,443, which issued to Blackwell for an invention entitled “Bowl and Slips Assembly With Improved Slip Inserts”, discloses a plurality of slipping inserts that are supported on carrier arms via a cantilevered connection. The carrier arms are pivotally mounted to a slip bowl to achieve a jaw-like action when gripping a piping. For the device as disclosed by Blackwell, however, the slipping inserts essentially hang from the carrier arms, and the spider of Blackwell cannot be inverted, lest the slip inserts fall away from the body.

[0008] U.S. Pat. No. 3,846,877, which issued to Spiri for an invention entitled “Well Slip Assembly”, discloses a slip mechanism for gripping a piping string in which one end of a slip assembly is attached to a guideway cut into a slip bowl and the other end of the slip assembly is attached to a lever arm outside of the bowl. For the device as disclosed by Spiri, however, the guideway is internal to the bowl and presents extraordinary repair problems if the slip assembly breaks at the attachment point within the guideway. As oil rigs are often located at remote land and sea locations, repairs must be easy to accomplish with a minimum of time and effort.

[0009] In light of the above, it is an object of the present invention to provide a pipe clamping device that can be used either in a normal or in an inverted position during snubbing operations. It is another object of the present invention to provide a pipe clamping device which moves along an exact path of travel to tightly clamp the pipe during operation. It is another object of the present invention to provide a spider with slip assemblies which maintain their adjustment setting when inverted to prevent undesired movement of the spider slip assemblies. Yet another object of the present invention is to provide a pipe clamping device which has easy access to the slip assemblies to facilitate repairs. It is another object of the present invention to provide a pipe clamping device which is relatively simple to use, is relatively easy to manufacture and is comparatively cost effective.

SUMMARY OF THE INVENTION

[0010] A well drilling pipe clamping apparatus of the present invention includes a body which is formed with an opening that extends completely through the body. The opening defines a longitudinal axis and allows for the pipe to be inserted into the apparatus for clamping. The opening is defined by a frusto-conical surface that is formed in the body.

[0011] A pair of guide plates are attached to the body so that they extend radially outward from the body. The guide plates are spaced-apart from each other and are also fixed to each other in a parallel relationship. Each guide plate is formed with an arch-shaped cam slot. A cam follower pin is transversely positioned between the guide plates and positioned in the cam slot so that the pin extends into both cam slots. Each guide plate is also formed with a retractor arm opening near the top edge of the plate The apparatus of the present invention further includes a retractor arm and a crankshaft. One end of the retractor arm is formed with an opening, and the retractor arm is placed between the two guide plates and maneuvered until the opening at the end of the retractor arm is aligned with the retractor arm openings in the guide plates. Next, the crankshaft is inserted through one guide plate, the retractor arm and the other guide plate. Both the retractor arm and the crankshaft are formed with a key slot. For assembly, the slots for the retractor arm and crankshaft are aligned and a key is inserted therein to fix the retractor arm to the crankshaft.

[0012] A pair of J-shaped guide arms are added to the above structure. Specifically, each guide arm is positioned next to a corresponding guide plate so the guide plates are between the guide arms. One end of each guide arm is attached to the cam follower pin. The other end of each guide arm is attached to the free end of the retractor arm.

[0013] The guide arms, guide plates, cam follower pins and retractor arms described above cooperate to define a cage for the apparatus of the present invention. Preferably, a second cage is assembled in the same manner and is mounted to the body opposite the body opening from the first cage.

[0014] The apparatus is further provided with a plurality of slip assemblies for gripping the pipe. Each slip has an arcuate outer surface and an arcuate inner surface with gripping teeth. At one end of the slip assembly, a dog ear structure extends radially outward from the outer arcuate surface, and the dog ear is placed between the guide arms and retractor arm and attached thereto in order to fix the slip assemblies to the cage. The slip assemblies are deployed in pairs so that two dog ears are located between the guide arms, while at the same time the retractor arm is located between the dog ears.

[0015] The cages of the apparatus are connected by a linkage to achieve a synchronized opening and closing action. The linkage is connected at one end to the crankshaft of one cage and at the other end to the crankshaft of the second cage. A hydraulic piston and cylinder device is connected to the linkage to move the linkage in translation. This translational motion of the linkage is converted to rotational motion of the crankshafts.

[0016] The rotation of the crankshafts causes the attached retractor arms to pivot, which further causes the guide arms to follow the motion of the retractor arms at one end of the guide arms. As the guide arm end connected to the retractor arm moves, the guide end connected to the cam follower pin also moves along a pate defined by the cam slots in the guide plates. As the guide arms move, the attached slip assemblies move until the arcuate outer surfaces of the assemblies contact the frusto-conical surface of the body. Once this occurs, the apparatus is in a closed position. When in the closed position, the arcuate teeth surfaces of the opposing cages define 360 degree surfaces for gripping a pipe that is inserted into the body opening .

[0017] For opening, the hydraulic means is operated to move the linkage in the opposite direction than that described above for closing the apparatus. The linkage causes the crankshafts to contra-rotate to pivot the retractor arms away from the body and to move the guide arms also away from the body. This causes the slip assemblies to move upward and outward from the body in a somewhat jaw-like action to place the apparatus in a open position.

[0018] The apparatus of the present invention further includes a plurality of resilient members for biasing the cages in an open position. Each guide plate merges into a finger extension which projects radially outward from the guide plate, and a spring shaft is transversely mounted between the two spaced-apart finger extensions. Each resilient member has one end connected to the spring shaft and another end that is connected to the cam follower pin. With the apparatus in a closed position, the cam follower pin is furthest from the spring shaft and the resilient members are in tension. As the apparatus moves toward an open position, the resilient members generate an additional force to urge the cam follower pin toward the outer portion of the cam slot, which further urges the guides arms and retractor arm toward an open position.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The novel features of this invention will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similar characters refer to similar parts, and in which:

[0020]FIG. 1 is a side elevational view of an oil well which shows a plurality of the pipe clamping apparatus of the present invention in an operational environment.

[0021]FIG. 2 is an exploded isometric view of the clamping apparatus of the present invention that shows the interconnective relationships between the component parts.

[0022]FIG. 3 is a top plan view of the body of the apparatus of FIG. 2.

[0023]FIG. 4 is a rear elevational view of the body of FIG. 3.

[0024]FIG. 5 is a front elevational view of the body of FIG. 3.

[0025]FIG. 6 is a right side elevational view of the body of FIG. 3, with portions cut away for clarity.

[0026]FIG. 7 is an isometric view of a cage for the apparatus of FIG. 2.

[0027]FIG. 8 is a side elevational view of the guide plate for the cage of FIG. 7.

[0028]FIG. 9 is an end elevational view of the cage of FIG. 7 which shows the cooperation of structure between the guide plate(s) and brace bars of the cage.

[0029]FIG. 10 is a side elevational view of a guide arm for the cage of FIG. 7.

[0030]FIG. 11 is a rear isometric view of a pair of slip assemblies for the apparatus of FIG. 2.

[0031]FIG. 12 is a front isometric view of a pair of slip assemblies for the apparatus of FIG. 2.

[0032]FIG. 13 is an exploded isometric view of the connector parts and teeth for the pair of slips shown in FIG. 11.

[0033]FIG. 14 is a side elevational view of the apparatus of FIG. 2 that shows the apparatus in a closed, clamping position, with portions of the body broken away for clarity.

[0034]FIG. 15 is the same view as FIG. 14 but with the apparatus in an open position.

WRITTEN DESCRIPTION OF THE PREFERRED EMBODIMENT

[0035] In brief overview, FIG. 1 shows somewhat diagrammatically a snubbing or hydraulic workover apparatus to be used for raising or lowering, while under pressure, a section of oil piping 600. As shown, oil piping 600 extends through well head structure 604 into well 606.

[0036] The well of FIG. 1 includes a plurality of “spiders” (the pipe clamping apparatus of the present invention) 10, of which spiders 10 a and 10 b are representative. The number of spiders used varies according to the length and/or diameter of the oil piping 600. In FIG. 1, spider 10 a is attached to the upper side of a stationary platform 612, while spider 10 b is carried at the lower side of a second, movable platform 614, in a relatively inverted position to spider 10 a.

[0037] As mentioned above, movable platform 614 is vertically movable between the full line and broken line positions of FIG. 1. Movable platform 614 is moved between the above positions by a number of hydraulic mechanisms 616. These mechanisms 616 include power cylinders 618 that are connected at a lower end to well head platform 617 and at an intermediate point to stationary platform 612.

[0038] For each mechanism, a piston 620 is slidably mounted within a respective power cylinder 618. The free end of each piston is attached to movable platform 614. As movable platform 614 is raised/lowered, spiders 10 a, 10 b are operated to selectively engage piping 600 in order to maintain control over the piping. For example, spider 10 a in FIG. 1 is in an open, retracted position, while spider 10 b is in a closed, engaged position to control any upward movement of piping 600. In this manner, the spiders can be deployed to control the motion of the piping as the mechanisms raise/lower the movable platform.

[0039] Referring now to FIGS. 2-15, the structure of the pipe clamping apparatus 10 is shown in greater detail. In these Figures (and as mentioned above), the clamping apparatus of the present invention is shown and is generally designated 10. The apparatus includes a body 12 that is oriented around vertical axis 14. The body includes a lower portion 18 that merges into a horseshoe-shaped upper portion 20. The upper portion includes a pair of opposing apertures for receiving slips 42 therethrough and terminates at a planar top surface 44 that is typically horizontally disposed during operation of the apparatus. Similarly, lower portion 18 terminates at a planar bottom surface 46 (FIGS. 5 and 6). This bottom surface is typically engaged against a horizontal surface of a stationary platform 612 or a movable platform 614 as described above and shown in FIG. 1.

[0040] The body further includes a gate 22 that, in combination with lower portion 18, completely surrounds vertical axis 14 and establishes an opening 16 in the body (See FIGS. 2 and 3). Tabs 25 extend outwardly from opposing sides of the gate, and a gate hole 24 is vertically formed through each tab. To removably attach the gate to the body, the lower portion is provided with four lower portion openings 26, two of which are shown in FIG. 1 (also shown in phantom in FIGS. 4 and 6). When the gate is positioned in place against the lower portion of the main section, the gate holes align with the lower portion openings. A pair of retaining pins 28 are inserted therein to secure the gate to the main section. The retaining pins are each attached to the body with a respective lightweight chain 30 for convenience of storage and to prevent loss of the retaining pins when the gate is not engaged with the lower portion of the main section.

[0041] The gate is provided with an inner beveled face 23. When the gate is attached to the body, beveled face 23 cooperates with lower portion inner surface 36 to create a frusto-conical shaped surface that tapers inwardly toward the bottom surface 46 of the body (See FIGS. 3, 6 and 15). The frusto-conical surface is shaped in the above manner to more effectively engage the outer arcuate surfaces 40 of a plurality of clamping slips 42 as more fully described below. The structure of the slips is also discussed in greater detail below.

[0042] The body 12 includes two opposing front lug projections 48 a, 48 b (FIGS. 2-5) which extend outwardly from the lower portion and are co-planar with each other. Similarly, rear lug projections 48 c, 48 d extend outwardly from the lower portion and are also co-planar with each other. Further, the respective planes containing the front lug projections and rear lug projections are parallel to each other. Each lug projection 48 a-d is formed with a respective upper opening 50 a-d and lower opening 52 a-d, to facilitate further assembly for the apparatus as detailed below.

[0043] Referring now primarily to FIGS. 2 and 7-10, the apparatus of the present invention includes two opposing cages 71 which are mounted to the body opposite from each other. Each cage comprises two guide plates 54 which are interconnected in a spaced-apart relationship by a plurality of spacer bars 70 so that the guide plates are parallel to each other.

[0044] Each guide plate is formed with a respective retractor arm opening 60 and a key slot 62 which extends radially outward from the retractor arm opening (FIG. 9). At the end of the guide plate opposite from retractor arm opening 60, the guide plate merges into a finger extension 64 projecting outwardly from the guide plate. The finger extension is formed with a finger extension opening 66 proximate its end. Each guide plate also is formed with a brace arm opening 67 near its bottom edge, as well as a plurality of space bar openings 68 for receiving the aforementioned spacer bars (FIGS. 8 and 9).

[0045] As shown in the Figures, each guide plate is also formed with a cam slot 58. The cam slot has an arch shape that begins at an outer low point 32 near the finger extension. The outer low point merges into slot apex 34 at about the mid-point of the plate. From the apex, the cam slot turns downward and terminates at an inner low point 36.

[0046] The clamping apparatus of the present invention is also provided with a plurality of somewhat J-shaped guide arms 56. As best seen in FIG. 10, guide arm 56 includes a lower guide arm end 72 that is formed with a lower guide arm opening 74. Opposite the guide arm from lower guide arm end 72, triangular end 76 of the guide arm flares out in a triangular shape and is formed with a first triangular end opening 78 and a second triangular end opening 80.

[0047] Two guide arms are slidably attached to each cage. To do this, a respective guide arm is positioned outwardly of each guide plate, as best seen in FIG. 7. Lower guide arm openings 74 for both guide arms are aligned with the cam slots on the guide plates. A cam follower pin 114 is inserted through, in sequence, the lower guide arm opening of the near guide arm, the cam slot for the near guide plate, the cam slot for the far guide plate and the lower guide arm opening for the far guide arm. Once inserted, the cam pin is slidably fixed in place within the cam slot with cotter pin 116, as best seen in FIG. 7. Other fasteners and/or methods of fastening, such as set screws, bolt and nut combinations and tack welding could also be used. With this configuration, the cam follower pin (and attached guide arms) are constrained to a path of motion defined by the cam slots of the guide plates.

[0048] At the triangular ends of the guide arms, upper and lower retainers 118 a, 118 b are inserted through the first guide arm openings and second guide arm openings, respectively. The upper and lower retainer retainers, as well as the triangular ends of the guide arms, interact with retractor arm 82 (FIGS. 2 and 7) in a manner to be described.

[0049] The cages for the clamping apparatus of the present invention further include at least two resilient members 120 per cage, as shown in the Figures. For attachment, inner resilient member end 122 of the spring is attached to the cam follower pin, while the outer end 124 is attached to a spring shaft 126 that extends transversely across the finger extensions of the guide plates. For attachment of the spring shaft to the finger extensions, the spring shaft 126 is inserted into finger extension openings 66 and fixed thereto in a manner known in the art.

[0050] As mentioned above, each cage includes a retractor arm 82 with a key end 84 and a slip end 88. The key end is formed with an alignment opening 86 that merges into a retractor arm key slot 87 (FIG. 7), while the slip end is formed with an oval-shaped hole 90. With this configuration, lower retainer 11 8 b is also inserted through the oval-shaped hole 90 of slip end 88, as shown in FIGS. 1 and 2. The cooperation of structure between the key end of the retractor arm, the cage and the body of the apparatus will be discussed in greater detail below.

[0051] The manner in which the cages are attached to the body is best appreciated by referring to FIG. 2. While the attachment of one cage is discussed, it is to be appreciated that the other cage is attached opposite opening 16 from the discussed cage in the same manner.

[0052] For assembly, a spacer 92 is inserted into the lower lug opening 52 a of front lug projection 48 a. Similarly, a spacer is inserted into lower lug opening 52 c of rear lug projection 48 c. For each spacer, one end (not shown in the FIGS. ) of brace arm 94 is secured to the spacer 92 and attached with brace arm fastener 96. Once attached, the two brace arms extend laterally outward from the body in a parallel, spaced-apart relationship.

[0053] The cage 71 is positioned between the spaced-apart brace arms 94. Next, the cage is maneuvered to align the brace arm openings 67 in the guide plates (See FIG. 8) with brace arm holes 98 proximate brace arm ends 100. Once aligned, a respective brace arm fastener 102 is inserted into the brace arm holes and brace arm opening to fix the cage to the brace arms (and, hence, to the body), as shown in FIG. 2. The fastener shown in FIG. 2 is a bolt and nut combination (only the bolt is shown). It is to be appreciated, however, that other fasteners are envisioned for the present invention, such as rivets or tack welds, for example, for attachment of the cage to the body as described above.

[0054] To pivotally attach the retractor arm to the cage, alignment opening 86 is aligned with upper lug opening 50 a for front lug projection 48 a, upper lug opening 50 c for rear lug projection 48 c and with retractor arm openings 60 in the guide plates. A crankshaft 106 is then inserted through, in sequence, upper lug opening 50 a for front lug projection 48 a, a retractor arm opening in the guide plate, alignment opening 86, another retractor arm opening on the opposing side of the body and upper lug opening 50 c for rear lug projection 48 c. Bushings and other similar means known in the art can be incorporated into upper lug openings 50 a, 50 b to facilitate rotation of the crankshaft in a manner known in the art.

[0055] To fix the retractor arm to the crankshaft, the clamping apparatus of the present invention includes an orientation key 108. The key fits into a notch 110 on the crankshaft, as well as into key slot 87 that merges outwardly from alignment opening 86. For assembly, notch 110 is aligned with corresponding key slot 87 and key 108 is placed therein.

[0056] As best seen in FIG. 7, crankshaft 106 includes a shaft portion 149 and a crankshaft arm 148 that projects substantially perpendicular to shaft portion 149. A stub post 136 further projects perpendicularly from crankshaft arm 148 and parallel to shaft portion 149. The stub post projects away from shaft portion 149 for reasons to be described.

[0057] When a second cage is fixed to body 12 opposite opening 16 from cage 71, the two crankshafts of the cages are connected to each other with a linkage 128. Each end 130 a, 130 b of the linkage is formed with a linkage opening 132 a, 130 b, and a stub post 136 for each respective crankshaft is inserted into the linkage openings 132 a and 132 b so that they are rotatable therein. Retaining clips, cotter pins, bolts or other means known in the art are then used to rotatably fix the stub posts within the linkage openings 132 a and 132 b to thereby prevent the linkage from slipping off of the stub posts of the crankshafts. Piston tab 134 projects outwardly from linkage end 130 a for connection with piston 141 as detailed below.

[0058] Pneumatic, hydraulic or mechanical means known in the art may be used to move the linkage. Preferably, a hydraulic cylinder 140 is used with piston 141 which is slidably mounted therein and which extends from first cylinder end 142, as shown in FIGS. 2, 14 and 15. Piston end 141 is connected to piston tab 134 of linkage 130. Second cylinder end 144 is fastened to a cylinder tab 146 on the body (shown in FIGS. 4 and 14-15). The cylinder has internal hydraulic mechanisms (not shown) that are known in the art for selectively causing translational movement of piston 141 in a manner known in the art.

[0059] Thus far, the cage(s) and body of the apparatus of the present invention have been discussed. As detailed above, the cage(s) and body cooperate to move the slips for selective engagement of the pipe. Now, the structure of the slips 42 will be discussed in greater detail. Referring primarily to FIGS. 11 -13 with respect to the structure of the slips, the slips have corresponding inner arcuate surfaces 152 with removable gripping plates 154 which engage the surface of a pipe when the apparatus is in the active clamping position. These gripping plates are provided with arcuate teeth 156 following generally the curvature of the outer arcuate surface 40 of the slip.

[0060] To enable replacement of a gripping plate when its teeth are worn, each slip is configured as shown in FIG. 13. Specifically, the external cylindrical surface 158 of the gripping plate is formed with a notch 160 which extends along the longitudinal extent of the gripping plate. Further, the plate has a ridge 162 along the outward radial edge of the top of the gripping plate.

[0061] For installation, external cylindrical surface 158 of the gripping plate is engaged against the inner arcuate surface 152 so that the ridge on the gripping plate fits into a complementary arcuate channel 164 on the slip. The gripping plate is maneuvered to align the notch of the gripping plate with a complementary longitudinal notch 165 on the inside surface of the slip. A rod 166 is inserted into the aligned notches. The rod rests against a bottom shoulder 168 of the slip. A retaining pin 170 is inserted into an opening (not shown) of the slip, to prevent the rod from inadvertently slipping out of the aligned notches. In this manner, the gripping plate is removably attached to the slip.

[0062] In order to mount the slip to the cage, each slip has a rigid mounting ear 172 projecting radially outwardly from the slip upper end portion. Each ear is desirably flat or planar and includes an upper ear opening 174 and a lower ear opening 176. The slips are assembled in pairs so that the ears of a pair of slips define corresponding adjacent planes that are about parallel with each other.

[0063] To mount the slips to the cage, a pair of slips is positioned between a pair of guide arms so that upper ear openings 174 are aligned with second triangular end openings 80. Slip end 88 of retractor arm 80 is positioned between the two slips and lower ear openings 176 are aligned with first triangular end openings 78 and with oval shaped hole 90 on the retractor arm. Upper retainer 11 8 a is passed through the second triangular end openings and upper ear openings. Lower retainer 118 b is passed through first triangular end openings 78, lower ear openings 176 and oval-shaped hole 90. Upper retainer 118 a and lower retainer 118 b are then tightened to fix the slips to the clamping apparatus of the present invention.

OPERATION

[0064] In the operation of the clamping apparatus of the present invention (from an open, retracted position), the hydraulic cylinder is activated in a manner known in the art to move piston 141 in translation, in a direction away from cylinder 140. As the piston moves, the attached linkage 132 also moves in translation. The translational motion of linkage 130 is converted into rotational motion of the crankshafts 136.

[0065] For each crankshaft, as the crankshaft turns, it rotates about axis 112 (FIGS. 2 and 7). Since key end 84 of retractor arm 82 is fixed to the crankshaft, key end 84 rotates with the crankshaft. This causes slip end 88 to pivot about the same axis. The location of the notch 110 for each crankshaft is located on opposite sides of the body to have a fixed, standard spatial relationship with each other and so that they contra-rotate to smoothly move the cages toward body opening 16 in a symmetrical fashion.

[0066] As the slip ends of the retractor arms pivot, the triangular ends of the guide arms also pivot. The pivoting of the triangular ends further cause the attached slips to pivot inwardly toward opening 16.

[0067] As the triangular ends of the guide arms pivot toward the body, the lower ends of the guide arms are also urged toward the body. More specifically, since the lower ends of the guide arms are attached to the cam follower pin, the cam follower pin is urged from the outer low point 32 of the cam slot 58 inwardly toward slot apex 34, and then further toward the inner lower point 36. This inward motion of the cam follower pin along the cam slot induces a reactive tension in resilient members 120.

[0068] When the cam follower pin for each cage is located at the inner low point of the cam slot, the outer arcuate surfaces of the slips engage the lower portion inner surface 36. Once this occurs, the slips are in a gripping position that is best seen in FIG. 14 for clamping a pipe, and the apparatus of the present invention is in a closed position.

[0069] To place the slips in an open, retracted position, the hydraulic cylinder is reversed to move piston 141 toward the cylinder. This causes each crankshaft to rotate in an opposite direction, which further causes the retractor arms to pivot outwardly from the body. As the retractor arms pivot outwardly, the attached triangular ends of the guide arms also pivot outwardly.

[0070] Simultaneous with the above actions, the cam follower pin follows an outward motion in the cam slot from the inner low point to the slot apex. At the slot apex, the tension in the resilient member provides an additional force. The additional force further urges the cam follower pin toward outer lower point 32. This force biases the slips in an open position and facilitates disengagement of the clamping apparatus from the pipe. As the cam follower pin moves toward the outer low point of the guide plates, the slips move upwardly and outwardly in a jaw-like action to open the apparatus and release the pipe. Because of the tension in the resilient members, the guide arms (and the attached slips) “snap” outwardly in a pivoting motion. Once the cam follower pins are at the outer lower point of the cam slot, the apparatus of the present invention is in an open position.

[0071] While the particular pipe clamping apparatus, as herein shown and disclosed in detail, is fully capable of obtaining the objects and providing the advantages above stated, it is to be understood that the presently preferred embodiments are merely illustrative of the invention. As such, no limitations are intended other than as defined in the appended claims. 

What is claimed is:
 1. An apparatus for clamping a pipe which comprises: a body having an opening for receiving said pipe, said opening extending through said body; a clamping means for selective engagement with said piping; and a camming means defining a path of travel for said clamping means, said camming means being fixedly attached to said body, said camming means being movably attached to said camming means.
 2. The apparatus of claim 1 wherein said camming means comprises at least one guide plate attached to said body proximate said opening, said guide plate projecting outwardly from said body and being formed with a cam slot.
 3. The apparatus of claim 2 wherein said camming means includes a cam follower pin fixedly attached to said clamping means, said pin projecting into said cam slot and being movable therein.
 4. The apparatus of claim 3 wherein said camming means further comprises: a retractor arm having a first retractor end pivotally mounted to said guide plate and having a second retractor end; and, at least one guide arm having a first guide arm end attached to said cam follower pin and having a second guide arm end attached to said second retractor end.
 5. The apparatus of claim 4 wherein said cam slot is arch-shaped and has an outer point, an apex and an inner point, said outer point being located further from said body than said apex, said apex being located further from said body than said inner point.
 6. The apparatus of claim 5 wherein said clamping means comprises at least slip assembly having an arcuate outer surface and an arched inner surface, said slip assembly being attached to said second retractor end and to said second guide arm end.
 7. The apparatus of claim 6 wherein said opening defines a longitudinal axis and wherein said body has an outer surface and a frusto-conical inner surface co-extensive with said longitudinal axis, and further wherein said apparatus is in a closed position when said arcuate outer surface engages said frusto-conical surface.
 8. The apparatus of claim 7 wherein said cam follower pin is located at said inner point when said apparatus is in said closed position.
 9. The apparatus of claim 7 wherein said apparatus has an open position when said arcuate surface is spaced above and is spaced radially outward from said frusto-conical surface.
 10. The apparatus of claim 9 wherein said cam follower pin is located at said outer point when said apparatus is in said open position.
 11. The apparatus of claim 10 further comprising a biasing means for biasing said cam follower pin toward said outer point when said apparatus is in said open position.
 12. The apparatus of claim 9 wherein said biasing means comprises at least one resilient member having a first resilient member end connected to said guide plate and having a second resilient member end attached to said cam follower pin.
 13. The apparatus of claim 12 wherein said guide plate, said cam follower pin, said retractor arm, said guide arm and said resilient member define a first cage for said apparatus.
 14. The apparatus of claim 13 further comprising two cage structures mounted opposite said opening from each other.
 15. The apparatus of claim 14 further comprising: a first crankshaft fixed to said first cage and rotatably mounted to said body; a second crankshaft fixed to said second cage and rotatably mounted to said body; and, a linkage for connecting said first crankshaft to said second crankshaft for simultaneously moving said first cage and said second cage between said open position and said closed position.
 16. An apparatus for clamping a pipe which comprises: a body having an opening for receiving said pipe, said opening extending through said body; at least one clamping means for selective engagement with said piping; and at least one cage mounted external to said body for defining a path of travel for said clamping means, said clamping means being fixed to said cage.
 17. The apparatus of claim 16 wherein said cage comprises two spaced-apart guide plates attached to said body to extend outwardly therefrom, each of said guide plates being oriented substantially parallel to each other and being formed with a corresponding cam slot.
 18. The apparatus of claim 17 further comprising: a cam follower pin extending from one of said guide plates to the other of said guide plates, said pin having a first pin end inserted into one of said cam slots and having a second pin end inserted into the other of said cam slots; a first guide arm having a first guide arm end attached to said first pin end and having a second guide arm attached to said clamping means; and, a second guide arm having a third guide arm end attached to said second pin end and having a fourth guide arm end attached to said clamping means.
 19. The apparatus of claim 16 wherein said opening has a longitudinal axis and wherein said body is formed with a truncated frusto-conical surface co-extensive with said axis, and wherein said clamping means comprises: a slip assembly, said slip assembly having an arcuate inner gripping surface, and arcuate outer surface, said apparatus being in a closed position when said arcuate outer surface is in contact with said frusto-conical surface.
 20. A method for raising and lowering a pipe for an oil rig which comprises the steps of: A) providing a plurality of snubbing spiders, each spider including a body with an opening for receiving said pipe, said opening extending through said body, each spider also having a plurality of slip assemblies for selective engagement with said piping, each slip assembly being connected to a cam follower pin, each spider also having a guide plate attached to said body, said guide plate being formed with a cam slot, each cam follower pin being inserted into said cam slot; B) engaging said piping with at least one of said spiders; C) inverting another of said spiders; D) gripping said piping with at least one of said inverted spiders; and, E) selectively releasing said spider and said inverted spider according to the desired movement direction of said piping. 